Narrow-band red phosphors for led lamps

ABSTRACT

A light emitting device (LED-Filament) comprises: a light-transmissive substrate; at least one blue LED chip mounted on a face of the light-transmissive substrate; and a photoluminescence material at least partially covering the at least one blue LED chip. The photoluminescence material comprises phosphor particles of at least one Group IIA/IIB selenide sulfide-based phosphor material that generates red light with a peak emission wavelength in a range of 600 nm to 640 nm and a full width at half maximum emission intensity of 50 nm to 55 nm. The LED-filament can be incorporated in a lamp, with a yellow to green-emitting phosphor that generates yellow to green light with a peak emission wavelength in a range of 520 nm to 570 nm, to provide light with a color temperature in a range of 1500 K to 4000 K and a General Color Rendering Index (CRI Ra) of greater than or equal to 90 and a CRI R9 greater than or equal to 50.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of priority to U.S.Provisional Patent Application No. 62/446,330, filed 13 Jan. 2017, whichis hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention are directed to narrow-band redphosphors for LED lamps, and more particularly, but not exclusively, toGroup IIA/IIB selenide sulfide-based phosphor materials forLED-filaments and LED-filament lamps.

BACKGROUND OF THE INVENTION

White light emitting LEDs (“white LEDs”) include one or morephotoluminescence materials (typically inorganic phosphor materials),which absorb a portion of the blue light emitted by the LED and re-emitlight of a different color (wavelength). The portion of the blue lightgenerated by the LED that is not absorbed by the phosphor materialcombined with the light emitted by the phosphor provides light whichappears to the eye as being white in color. Due to their long operatinglife expectancy (>50,000 hours) and high luminous efficacy (100 lm/W andhigher) white LEDs are rapidly being used to replace conventionalfluorescent, compact fluorescent and incandescent lamps. LED lamps(bulbs) are typically constructed from a small number of high-intensitywhite LEDs.

Recently, LED-filament lamps have been developed that compriseLED-filaments that closely resemble the filament of a traditionalincandescent lamp. The LED-filaments, which are typically about an inchlong, comprise COG (Chip-On-Glass) devices having a plurality oflow-power LED chips mounted on a light-transmissive (transparent) glasssubstrate. The LED-filaments are encased in a phosphor-impregnatedencapsulant, such as silicone. Typically, LED-filament lamps areconfigured to generate “warm white” light with a CCT (Correlated ColorTemperature) of 2700 K to 3000 K with a General Color Rendering Index(CRI Ra) of up to 80. A need exists for LED-filament lamps having a CRIRa of at least 90. While the CRI Ra of white LEDs can be increased byincluding an orange or red emitting phosphor, it is found that theluminous efficacy decreases. There is a need to provide an LED-Filamentlamp that has a CRI Ra of 90 and which has a smaller decrease inluminous efficacy compared with packaged white LEDs.

SUMMARY OF THE INVENTION

Embodiments of the invention concern LED-filaments and LED-filamentlamps that comprise a narrow-band red phosphor that generates red lightwith a peak emission wavelength in a range of 600 nm to 640 nm and afull width at half maximum emission intensity of 50 nm to 55 nm. Inparticular, the narrow-band red phosphor comprises particles of at leastone Group IIA/IIB selenide sulfide-based phosphor material, such as forexample CaSe_(1-x)S_(x):Eu (CSS phosphor). Compared with knownLED-filament lamps comprising a CASN red nitride phosphor (CalciumAluminum Silicon Nitride), LED-filaments and LED-filament lamps inaccordance with the invention comprising a CSS phosphor are found to becapable of generating light having i) a CRI Ra of 90 and greater, ii) aCRI R9 up to about 55, and iii) a more stable chromaticity (quality oflight color) during a stabilization period after turn-on while havingsubstantially the same efficacy as LED-filament lamps comprising a CASNphosphor.

According to an embodiment, a light emitting device comprises: alight-transmissive substrate; at least one blue LED chip mounted on aface of the light-transmissive substrate; and a photoluminescencematerial at least partially covering the at least one blue LED chip, thephotoluminescence material comprising phosphor particles of at least oneGroup IIA/IIB selenide sulfide-based phosphor material; wherein thephosphor particles generate red light with a peak emission wavelength ina range of 600 nm to 640 nm and a full width at half maximum emissionintensity of 50 nm to 55 nm. The photoluminescence material cancompletely cover exposed light emitting surfaces of the at least oneblue LED chip.

In an embodiment, the Group IIA/IIB selenide sulfide-based phosphormaterial has a composition MSe_(1-x)S_(x):Eu, wherein M is at least oneof Mg, Ca, Sr, Ba and Zn and 0<x<1.0. In other embodiments, the GroupIIA/IIB selenide sulfide-based phosphor material can have a compositionMS_(x)Se_(y)A_(z):Eu, wherein M is at least one of Mg, Ca, Sr and Ba, Acomprises one or more of carbon, nitrogen, boron, phosphorous and amonovalent combining group NCN (cyanamide), 0<z≤0.05, and 0.8<x+y<1.25.

The phosphor particles can generate red light with a peak emissionwavelength in a range of 624 nm to 628 nm. In some embodiments, thephosphor particles generate red light with a peak emission wavelength ofabout 626 nm.

To improve reliability of the light emitting device, the phosphorparticles can comprise a dense impermeable coating on individual ones ofsaid phosphor particles. The dense impermeable coating material cancomprise one or more materials such as for example aluminum oxide,silicon oxide, titanium oxide, zinc oxide, magnesium oxide, zirconiumoxide, boron oxide, chromium oxide, calcium fluoride, magnesiumfluoride, zinc fluoride, aluminum fluoride and/or titanium fluoride. Insome embodiments the coating material can comprise amorphous alumina.

In an embodiment, the light emitting device is characterized by a CRI Raof greater than or equal to 90. Moreover, the light emitting device canbe further characterized by a CRI R9 of greater than or equal to 50.

In some embodiments, the Group IIA/IIB selenide sulfide-based phosphorparticles can comprise first particles with a first peak emissionwavelength and second particles with a second peak emission wavelength.In some embodiments, the first peak emission wavelength is in a range of624 nm to 628 nm and the second peak emission wavelength is in a rangeof 630 nm to 638 nm. LED-filaments and LED-filament lamps that comprisea mixture of at least two Group IIA/IIB selenide sulfide-based phosphorparticles having different peak emission wavelengths can, compared withan LED-filament comprising a single CSS phosphor, have a more stablechromaticity (quality of light color) during the stabilization periodafter lamp turn-on, increase the luminous efficacy while stillmaintaining a CRI Ra of at least 90 and exhibit only a minimal decreasein CRI R9. In an embodiment, the first peak emission wavelength is about626 nm and the second peak emission wavelength is about 634 nm. Inembodiments comprising first and second particles, the light emittingdevice can be characterized by a CRI Ra of greater than or equal to 90and a CRI R9 of greater than or equal to 50.

The photoluminescence material can further comprise particles of ayellow to green-emitting phosphor that generates yellow to green lightwith a peak emission wavelength in a range of 520 nm to 570 nm. In someembodiments, the yellow to green-emitting phosphor generates green lightwith a peak emission wavelength in a range of 520 nm to 540 nm. Theyellow to green-emitting photoluminescence material can comprise a GYAG(Green-emitting YAG) phosphor of general composition Y₃(Al,Ga)₅O₁₂:Ceand/or comprise a GAL (Green Aluminate) phosphor of general compositionLu₃Al₅O₁₂:Ce.

Typically, the at least one blue LED chip comprises an array of blue LEDchips such as for example a linear array of blue LED chips. In someembodiments, the light emitting device further comprises at least onesecond LED chip or array of second LED chips mounted on a second face ofthe light-transmissive substrate, said photoluminescence material atleast partially covering said at least one or array of second blue LEDchips. The light-transmissive substrate can have a transmittance in arange of 20% to 100% in the visible light spectrum and can comprisemagnesium oxide, sapphire, aluminum oxide, quartz glass, aluminumnitride or diamond. The light-transmissive substrate can be elongate inform, for example linear. The photoluminescence material can completelycover said at least one or array of second blue LED chips.

According to an embodiment, a lamp comprises: a light-transmissiveenvelope; and at least one light emitting device located within thelight-transmissive envelope, the light emitting device comprising: (1) alight-transmissive substrate; (2) at least one blue LED chip mounted ona face of the light-transmissive substrate; and (3) a photoluminescencematerial at least partially covering the at least one blue LED chip, thephotoluminescence material comprising: (a) phosphor particles of a GroupIIA/IIB selenide sulfide-based phosphor material that generates redlight with a peak emission wavelength in a range of 600 nm to 640 nm anda full width at half maximum emission intensity of 50 nm to 55 nm; and(b) phosphor particles of a yellow to green-emitting phosphor thatgenerates yellow to green light with a peak emission wavelength in arange of 520 nm to 570 nm; wherein the lamp is operable to generatelight with a color temperature in a range of 1500 K to 4000 K and a CRIRa of greater than or equal to 90. The lamp can be further characterizedby generating light with a CRI R9 of greater than or equal to 50. Thephotoluminescence material can completely cover said at least one blueLED chip.

In an embodiment, the Group IIA/IIB selenide sulfide-based phosphormaterial has a composition MSe_(1-x)S_(x):Eu, wherein M is at least oneof Mg, Ca, Sr, Ba and Zn and 0<x<1.0. In other embodiments, the GroupIIA/IIB selenide sulfide-based phosphor material can have a compositionMS_(x)Se_(y)A_(z):Eu, wherein M is at least one of Mg, Ca, Sr and Ba, Acomprises one or more of carbon, nitrogen, boron, phosphorous and amonovalent combining group NCN (cyanamide), 0<z≤0.05, and 0.8<x+y<1.25.

The Group IIA/IIB selenide sulfide-based phosphor particles phosphorparticles can generate red light with a peak emission wavelength in arange of 624 nm to 628 nm. In some embodiments, the phosphor particlesgenerate red light with a peak emission wavelength of about 626 nm.

To improve reliability of the light emitting device, the Group IIA/IIBselenide sulfide-based phosphor particles phosphor particles cancomprise a dense impermeable coating on individual ones of said phosphorparticles. The dense impermeable coating can comprise one or morematerials such as for example aluminum oxide, silicon oxide, titaniumoxide, zinc oxide, magnesium oxide, zirconium oxide, boron oxide,chromium oxide, calcium fluoride, magnesium fluoride, zinc fluoride,aluminum fluoride and/or titanium fluoride. In some embodiments, thecoating material can comprise amorphous alumina.

In some embodiments, the Group IIA/IIB selenide sulfide-based phosphorparticles can comprise first particles with a first peak emissionwavelength and second particles with a second peak emission wavelength.In some embodiments, the first peak emission wavelength is in a range of624 nm to 628 nm and the second peak emission wavelength is in a rangeof 630 nm to 638 nm. In an embodiment, the first peak emissionwavelength is about 626 nm and the second peak emission wavelength isabout 634 nm. In embodiments comprising first and second particles, thelight emitting device can be characterized by a CRI Ra of greater thanor equal to 90 and a CRI R9 of greater than or equal to 50.

In some embodiments, the yellow to green-emitting phosphor particlesgenerate the light with a peak emission wavelength in a range of 520 nmto 540 nm. The yellow to green-emitting phosphor particles can comprisea garnet structured material such as a GYAG phosphor (Green-emittingYAG) of general composition Y₃(Al,Ga)₅O₁₂:Ce and/or a GAL phosphor(Green ALuminate) of general composition Lu₃Al₅O₁₂:Ce.

In some embodiments, the light-transmissive envelope is filled with aninert gas, such as helium. Inclusion of an inert gas can aid indissipating heat generated by the light emitting device.

Typically, the at least one blue LED chip comprises an array of blue LEDchips such as for example a linear array of blue LED chips. In someembodiments, the light emitting device further comprises at least onesecond LED chip, or an array of second LED chips, mounted on a secondface of the light-transmissive substrate, said photoluminescencematerial at least partially covering said at least one second blue LEDchip. The light-transmissive substrate can have a transmittance in arange of 20% to 100% in the visible light spectrum and can comprisemagnesium oxide, sapphire, aluminum oxide, quartz glass, aluminumnitride or diamond. The light-transmissive substrate can be elongate inform, for example linear in form. The photoluminescence material cancompletely cover said at least one second blue LED chip.

According to another embodiment, a light emitting device comprises: alight-transmissive substrate; at least one blue LED chip mounted on aface of the light-transmissive substrate; and a photoluminescencematerial at least partially covering the at least one blue LED chip, thephotoluminescence material comprising phosphor particles of two GroupIIA/IIB selenide sulfide-based phosphor materials; wherein the phosphorparticles generate red light with a peak emission wavelength in a rangeof 600 nm to 640 nm and a full width at half maximum emission intensityof 50 nm to 55 nm. The phosphor particles can comprise first particleswith a first peak emission wavelength in a range of 624 nm to 628 nm andsecond particles with a second peak emission wavelength in a range of630 nm to 638 nm. The photoluminescence material can completely coverexposed light emitting surfaces of the at least one blue LED chip.

According to another embodiment, a lamp comprises: a light-transmissiveenvelope; and at least one light emitting device located within thelight-transmissive envelope, the light emitting device comprising: (1) alight-transmissive substrate; (2) at least one blue LED chip mounted ona face of the light-transmissive substrate; and (3) a photoluminescencematerial at least partially covering the at least one blue LED chip, thephotoluminescence material comprising: (a) phosphor particles of twoGroup IIA/IIB selenide sulfide-based phosphor materials that generatesred light with a peak emission wavelength in a range of 600 nm to 640 nmand a full width at half maximum emission intensity of 50 nm to 55 nm;and (b) phosphor particles of a yellow to green-emitting phosphor thatgenerates yellow to green light with a peak emission wavelength in arange of 520 nm to 570 nm; wherein the lamp is operable to generatelight with a color temperature in a range of 1500 K to 4000 K and a CRIRa of greater than or equal to 90. The lamp can be further characterizedby generating light with a CRI R9 of greater than or equal to 50. Thephotoluminescence material can completely cover said at least one blueLED chip.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 shows normalized emission spectra of CSS (CaSe_(1-x)S_(x):Eu)narrow-band red phosphors for differing ratios of S/Se;

FIG. 2 is a schematic representation of a phosphor particle coatingapparatus;

FIGS. 3A and 3B respectively illustrate partial cross-sectional A-A sideand plan views of a four LED-filament A-Series (A19) lamp in accordancewith an embodiment of the invention;

FIGS. 4A and 4B illustrates schematic cross-sectional B-B side andpartial cutaway plan views of an LED-filament in accordance with anembodiment of the invention for use in the lamp of FIGS. 3A and 3B;

FIGS. 5A and 5B respectively illustrate partial cross-sectional C-C sideand plan views of a four LED-filament B-Series (Bullet B11) lamp inaccordance with an embodiment of the invention;

FIG. 6 illustrates a partial cross-sectional side view of a fourLED-filament B-Series (B11) lamp in accordance with an embodiment of theinvention;

FIG. 7 shows test data, luminous flux (lm) versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) green aluminate phosphor (GAL535)+narrow-band red phosphor (CSS626)and ii) green aluminate phosphor (GAL 535)+red nitride phosphor(CASN630);

FIG. 8 shows test data, luminous efficacy (lm/W) versus time (s) afterlamp turn-on, for a four LED-filament A19 lamp with LED-filamentscomprising i) green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS626) and ii) green aluminate phosphor (GAL535)+red nitride phosphor(CASN630);

FIG. 9 shows test data, Color Rendering Index (CRI) Ra versus time (s)after lamp turn-on, for a four LED-filament A19 lamp with LED-filamentscomprising i) green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS626) and ii) green aluminate phosphor (GAL535)+red nitride phosphor(CASN630);

FIG. 10 shows test data, chromaticity CIE x versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) green aluminate phosphor (GAL535)+narrow-band red phosphor (CSS626)and ii) green aluminate phosphor (GAL535)+red nitride phosphor(CASN630);

FIG. 11 shows test data, chromaticity CIE y versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) green aluminate phosphor (GAL535)+narrow-band red phosphor (CSS626)and ii) green aluminate phosphor (GAL535)+red nitride phosphor(CASN630);

FIG. 12 shows reliability data, relative luminous flux (%) versus time(hours), for a four LED-filament A19 lamp with LED-filaments comprisinggreen aluminate phosphor (GAL535)+narrow-band red phosphor (CSS628);

FIG. 13 shows reliability data, change of chromaticity ΔCIE x versustime (hours), for a four LED-filament A19 lamp with LED-filamentscomprising green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS628);

FIG. 14 shows reliability data, change of chromaticity ΔCIE y versustime (hours), for a four LED-filament A19 lamp with LED-filamentscomprising green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS628);

FIG. 15 shows test data, luminous efficacy (lm/W) versus time (s) afterlamp turn-on, for a four LED-filament B11 lamp with LED-filamentscomprising i) green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS626), ii) green aluminate phosphor (GAL535)+narrow-band red phosphor(mixture: 90 wt. % CSS626 & 10 wt. % CSS634), and iii) green aluminatephosphor (GAL535)+narrow-band red phosphor (mixture: 70 wt. % CSS626 &30 wt. % CSS634);

FIG. 16 shows test data, Color Rendering Index (CRI) Ra versus time (s)after lamp turn-on, for a four LED-filament B11 lamp with LED-filamentscomprising i) green aluminate phosphor (GAL535)+narrow-band red phosphor(CSS626), ii) green aluminate phosphor (GAL535)+narrow-band red phosphor(mixture: 90 wt. % CSS626 & 10 wt. % CSS634), and iii) green aluminatephosphor (GAL535)+narrow-band red phosphor (mixture: 70 wt. % CSS626 &30 wt. % CSS634);

FIG. 17 shows test data, chromaticity CIE x versus time (s) after lampturn-on, for a four LED-filament B11 lamp with LED-filaments comprisingi) green aluminate phosphor (GAL535)+narrow-band red phosphor (CSS626),ii) green aluminate phosphor (GAL535)+narrow-band red phosphor (mixture:90 wt. % CSS626 & 10 wt. % CSS634), and iii) green aluminate phosphor(GAL535)+narrow-band red phosphor (mixture: 70 wt. % CSS626 & 30 wt. %CSS634); and

FIG. 18 shows test data, chromaticity CIE y versus time (s) after lampturn-on, for a four LED-filament B11 lamp with LED-filaments comprisingi) green aluminate phosphor (GAL535)+narrow-band red phosphor (CSS626),ii) green aluminate phosphor (GAL535)+narrow-band red phosphor (mixture:90 wt. % CSS626 & 10 wt. % CSS634), and iii) green aluminate phosphor(GAL535)+narrow-band red phosphor (Mixture: 70 wt. % CSS626 & 30 wt. %CSS634).

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples of the invention so as to enable those skilled in the art topractice the invention. Notably, the figures and examples below are notmeant to limit the scope of the present invention to a singleembodiment, but other embodiments are possible by way of interchange ofsome or all of the described or illustrated elements. Moreover, wherecertain elements of the present invention can be partially or fullyimplemented using known components, only those portions of such knowncomponents that are necessary for an understanding of the presentinvention will be described, and detailed descriptions of other portionsof such known components will be omitted so as not to obscure theinvention. In the present specification, an embodiment showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments including aplurality of the same component, and vice-versa, unless explicitlystated otherwise herein. Moreover, applicants do not intend for any termin the specification or claims to be ascribed an uncommon or specialmeaning unless explicitly set forth as such. Further, the presentinvention encompasses present and future known equivalents to the knowncomponents referred to herein by way of illustration.

The present invention includes light emitting devices and lampsincluding these light emitting devices. According to some embodiments, alight emitting device may comprise: a light-transmissive substrate; atleast one blue LED chip mounted on a face of the light-transmissivesubstrate; and a photoluminescence material at least partially coveringthe at least one blue LED chip, the photoluminescence materialcomprising phosphor particles of at least one Group IIA/IIB selenidesulfide-based phosphor material; wherein the phosphor particles generatered light with a peak emission wavelength in a range of 600 nm to 640 nmand a Full Width at Half Maximum (FWHM) emission intensity of 50 nm to55 nm. The photoluminescence material can completely cover said at leastone blue LED chip.

The lamps according to some embodiments may comprise: alight-transmissive envelope; and at least one light emitting devicelocated within the light-transmissive envelope, the light emittingdevice comprising: (1) a light-transmissive substrate; (2) at least oneblue LED chip mounted on a face of the light-transmissive substrate; and(3) a photoluminescence material at least partially covering the atleast one blue LED chip, the photoluminescence material comprising: (a)phosphor particles of a Group IIA/IIB selenide sulfide-based phosphormaterial that generates red light with a peak emission wavelength in arange of 600 nm to 640 nm and a full width at half maximum emissionintensity of 50 nm to 55 nm; and (b) phosphor particles of a yellow togreen-emitting phosphor that generates yellow to green light with a peakemission wavelength in a range of 520 nm to 570 nm; wherein the lamp isoperable to generate light with a color temperature in a range of 1500 Kto 4000 K and a CRI Ra of greater than or equal to 90. Thephotoluminescence material can completely cover said at least one blueLED chip.

Some examples of the Group IIA/IIB selenide sulfide-based phosphormaterial of the present invention are described below, and for eachexample the material may be phosphor particles or coated phosphorparticles. These phosphors are narrow-band red phosphors and haveemission characteristics such as shown in FIG. 1, and described in moredetail below.

Narrow-Band Red Phosphors: CSS Phosphors

A first example of a Group IIA/IIB selenide sulfide-based phosphormaterial has a composition MSe_(1-x)S_(x):Eu, wherein M is at least oneof Mg, Ca, Sr, Ba and Zn and 0<x<1.0. A particular example of thisphosphor material is CSS phosphor (CaSe_(1-x)S_(x):Eu). Details of CSSphosphors are provided in co-pending U.S. patent application Ser. No.15/282,551 filed 30 Sep. 2016, which is hereby incorporated by referencein its entirety. It is envisaged that the CSS narrow-band red phosphorsdescribed in U.S. patent application Ser. No. 15/282,551 can be used inthe present invention. FIG. 1 shows normalized emission spectra of CSSphosphors for differing ratios of S/Se, the emission peak can be tunedfrom 600 nm to 650 nm by the ratio of S/Se in the composition andexhibits a narrow-band red emission spectrum with Full Width HalfMaximum (FWHM) typically in the range from ˜48 nm to ˜60 nm (longerwavelength typically has a larger FWHM value). For comparison, a CASNred nitride phosphor (Calcium Aluminum Silicon Nitride basedphosphor—general composition CaAlSiN₃:Eu²⁺) typically has a FWHM of ˜80nm. As is known, CASN red phosphors are commonly used in LEDapplications. Note that x varies over a range from about 0.05 to about0.8 for the compositions shown in FIG. 1—the higher peak wavelengthscorresponding to the larger values of x; that is, as the amount of Sincreases this shifts the emission peak to a higher wavelength. Notethat the notation CSS604 used herein represents the phosphor type (CSS)followed by the peak emission wavelength in nanometers (604). The samenotation rule applies to the other phosphor types, such as CSS615 andCSS624 for example.

CSS phosphor particles are synthesized from purified CaSeO₄ and CaSO₄ ina mild H₂ (gas) environment (for example ˜5% H₂/N₂). Herein, unlessotherwise specified, CSS phosphor samples used in the examples have acomposition of CaSe_(1-x)S_(x):Eu withx˜0.2.

Narrow-Band Red Phosphors: Coated CSS Phosphors

The CSS phosphor particles can be coated with one or more oxides, forexample: aluminum oxide (Al₂O₃), silicon oxide (SiO₂), titanium oxide(TiO₂), zinc oxide (ZnO), magnesium oxide (MgO), zirconium oxide (ZrO₂),boron oxide (B₂O₃) or chromium oxide (CrO). Alternatively and/or inaddition, the narrow-band red phosphor particles may be coated with oneor more flourides, for example: calcium fluoride (CaF₂), magnesiumfluoride (MgF₂), zinc fluoride (ZnF₂), aluminum fluoride (AlF₃) ortitanium fluoride (TiF₄). In embodiments, the coatings may be a singlelayer, or multiple layers with combinations of the aforesaid coatings.The combination coatings may be coatings with an abrupt transitionbetween the first and second materials, or may be coatings in whichthere is a gradual transition from the first material to the secondmaterial thus forming a zone with mixed composition that varies throughthe thickness of the coating.

The particles can be coated by a CVD process in a fluidized bed reactor.FIG. 2 is a schematic representation of a phosphor particle coatingapparatus. Reactor 20 comprises a porous support disc 22, over whichphosphor powder 24 is held, and inlets 26 and 28 for metal organicprecursor and water vapor, respectively. The thickness of the coatingmay typically be in the ranges 100 nm to 5 μm, 50 nm to 100 nm, 100 nmto 500 nm, 500 nm to 1 μm, or 1 μm to 2 μm. Coated CSS narrow-band redphosphor particle samples used in the examples herein are coated withapproximately 1 μm of amorphous alumina (Al₂O₃).

In the case of alumina coatings, the coatings comprise a dense amorphousoxide coating layer on the CSS phosphor particle surface withoutpinholes (pinhole-free), that is a water impermeable coating.

In a typical coating process, the phosphor powder sample was loaded intothe reactor and heated to 100-250° C., preferably 200° C., under N₂ gasflow. When an oxide coating is to be deposited, a metal organic oxideprecursor MO such as TrimethylAluminum (TMA), Titanium tetra-chloride(TiCl₄), Silicon tetra-chloride (SiCl₄), or DimethylZinc (DMZ) wasintroduced in to the reactor 20 through inlet 26 with a N₂ carrier gasthrough a bubbler. H₂O vapor was also introduced into the reactor 20through inlet 28 to react with the metal oxide precursor to form oxidecoating layers on phosphor particles. Complete fluidization of theparticles being coated (from gas flow optimization, etc.) without anydead space is important to ensure homogeneous coating of all phosphorparticles. In a typical coating conducted at 200° C., for a 250 gphosphor particle loading of the reactor, the coating was produced witha metal oxide precursor feeding rate of 1 to 10 g/hour for 4 hours,while feeding H₂O at a rate of 2 to 7 g/hour. These conditions canproduce dense and pinhole free coatings and these conditions are able toproduce dense substantially pin-hole free coatings of uniform thickness,with a theorized percentage solid space (percentage bulk density) ofgreater than 95% and in embodiments greater than 97% and in embodimentsgreater than 99%. In this patent specification, percentage solidspace=(bulk density of the coating/density of the material within asingle particle)×100. It will be understood that the percentage solidspace (% solid space) provides a measure of the porosity of the coatingresulting from pinholes.

A variation of the phosphor particle coating apparatus of FIG. 2 fordepositing a fluoride coating comprises introducing a metal organicfluoride MF precursor in to the reactor 20 through inlet 26 with a N₂carrier gas through a bubbler. When depositing a fluoride coating no H₂Ois introduced into the reactor. In other respects, coating with afluoride is analogous to coating with an oxide as described above.

Narrow-Band Red Phosphors: Doped-CSS Phosphors

A second example of a Group IIA/IIB selenide sulfide-based phosphormaterial has a composition MS_(x)Se_(y)A_(z):Eu, wherein M is at leastone of Mg, Ca, Sr and Ba, A comprises one or more of carbon, nitrogen,boron, phosphorous and a monovalent combining group NCN (cyanamide),0<z≤0.05, and 0.8<x+y<1.25. A particular example of this phosphormaterial is a doped-CSS phosphor (CaS_(x)Se_(y)A_(z):Eu). Details ofthese doped-CSS phosphors are provided in co-pending U.S. patentapplication Ser. No. 15/075,080 filed 18 Mar. 2016 which is herebyincorporated by reference in its entirety. It is envisaged that thedoped-CSS phosphors described in co-pending U.S. patent application Ser.No. 15/075,080 can be used in the present invention. More generally, anarrow-band red phosphor can have a general compositionMS_(x)Se_(y)A_(z):Eu, wherein M is at least one of Mg, Ca, Sr and Ba, Ais at least one of C, N, B, P, and the monovalent combining groupNCN(cyanamide), and can further include one or more of O, F, Cl, Br andI. It can be that (1) 0.8<x+y<1.25 (where x≥0 and y≥0.1) and 0<z≤0.05,and it can be that (2) x+y is not equal to 1, x≥0, y≥0.1 and 0<z≤0.05,and it can be that (3) 1.0<x+y<1.25 (where x≥0 and y≥0.1) and 0<z≤0.05,and it can be that (4) x, y and z are determined strictly by chargebalancing. The narrow-band red phosphor can have a particle sizedistribution defined by D₅₀ in the range of 3 to 45 μm (microns), endpoints included, and it can be that D₅₀ in the range of 5 to 25 μm(microns), end points included. It is expected that the element A may befound in the phosphor material in one or more of the followingpositions: an interstitial position, a substitutional position, on agrain boundary or crystal surface, or within a second phase (such aswithin calcium fluoride). Although the doped-CSS phosphors can comprisephosphor compounds in which M is one or more alkaline earth metals, someamount of other metals such as zinc, lithium or cadmium can substitutefor some of the alkaline earth metal.

Synthesis of Doped-CSS Phosphors (MS_(x)Se_(y)A_(z):Eu) Example 1:Synthesis of 120 g of CaSeO₄ with 0.3 wt. % Eu₂O₃

After dissolving 83.4 g SeO₂ in 300 ml of de-ionized water in a beaker,45.0 g of 30% H₂O₂ solution is slowly added, then stirred for about 1hour. Ammonium hydroxide (29 wt. %) is then slowly added to the solutionuntil the pH reached approximately 10—this is solution #1.

110.0 g of CaCl₂.2H₂O is dissolved in 450 ml of ethanol in anotherbeaker, then 0.40 g of Eu₂O₃ powder is added, followed by 36% HCl whichis slowly added until the solution became clear—this is solution #2.

The solution of (NH₄)₂SeO₄ (solution #1) is added dropwise to solution#2 precipitating white crystals; the solution with precipitates isstirred for about 2 hours, then the solution is filtered and theprecipitates are dried at 80° C.

Example 2: Synthesis of Doped-CSS Phosphors(CaS_(0.25-z)Se_(0.75)C_(z)Eu_(0.003))

30 g of white CaSeO₄ with 0.3 wt. % Eu powder is mixed with 1.2 g ofsulfur powder and 1.2 g powdered carbon (such as Alfa Aesar: carbonblack, 99.9+%). The mixture is put in an alumina crucible with analumina cover and fired at 600° C. for 2 hours under 5% hydrogenbalanced with nitrogen, then the temperature is increased to 900° C. for4 hours. Furthermore, amounts of LiF, NH₄Cl, CaCl₂ or NH₄Br can also beadded as a flux. It can be that 0.9 g of boric acid is used in place ofthe powdered carbon to make MS_(x)Se_(y)B_(z):Eu phosphors. Similarly,calcium nitride, phosphorus pentasulfide and calcium cyanamide can beused in place of carbon as sources of N, P and NCN in the phosphormaterial.

Example 3: Washing as-Synthesized Doped-CSS Phosphors(CaS_(0.25-z)Se_(0.75)C_(z)Eu_(0.003))

The above as-synthesized phosphors are ground in a ceramic mortar, thenplaced in 600 ml of methanol solution in a 1.0 liter beaker and stirredfor 1 hour, then the phosphor particles are allowed to settle, thesolvents are decanted off the phosphor particles, and the particles aredried.

As with CSS phosphors, the doped-CSS phosphor can be coated in the samemanner and with the same materials detailed above.

LED-Filament Lamps: A-Series (A19) Lamps

FIGS. 3A and 3B respectively illustrate a partial cross-sectional sideview through A-A and a partial cutaway plan view of an LED-filamentA-Series lamp (bulb) 100 in accordance with an embodiment of theinvention. The LED-filament lamp 100 is intended to be an energyefficient replacement for an incandescent A19 light bulb and isconfigured to generate 550 lm of light with a CCT (Correlated ColorTemperature) of 2700 K and a CRI Ra of 90 and CRI R9>50. TheLED-filament lamp is nominally rated at 4 W. As is known, an A-serieslamp is the most common lamp type and an A19 lamp is 2⅜ inches (19/8)wide at its widest point and approximately 4⅜ inches in length.

The LED-filament lamp 100 comprises a connector base 110, alight-transmissive glass envelope 120; a glass LED-filament support(stem) 130 and four LED-filaments 140 a, 140 b, 140 c, 140 d.

In some embodiments, the LED-filament lamp 100 can be configured foroperation with a 110V (r.m.s.) AC (60 Hz) mains power supply as used inNorth America. As illustrated, the LED-filament lamp 100 can comprise anE26 (ϕ26 mm) connector base (Edison screw lamp base) 110 enabling thelamp to be directly connected to a mains power supply using a standardelectrical lighting screw socket. It will be appreciated that dependingon the intended application other connector bases can be used such as,for example, a double contact bayonet connector (i.e. B22d or BC) as iscommonly used in the United Kingdom, Ireland, Australia, New Zealand andvarious parts of the British Commonwealth or an E27 (ϕ27 mm) screw base(Edison screw lamp base) as used in Europe. The connector base 110 canhouse rectifier or other driver circuitry (not shown) for operating theLED-filament lamp.

The light-transmissive glass envelope 120 is attached to the connector110 and defines a hermetically sealed volume 150 in which theLED-filaments 140 a to 140 d are located. The envelope 120 canadditionally incorporate or have a layer of a light diffusive(scattering) material such as for example particles of Zinc Oxide (ZnO),titanium dioxide (TiO₂), barium sulfate (BaSO₄), magnesium oxide (MgO),silicon dioxide (SiO₂) or aluminum oxide (Al₂O₃).

The LED-filaments 140 a to 140 d, which are linear (elongate) in form,are oriented such that each runs in a direction that is generallyparallel to an axis 250 of the lamp 100. The LED-filaments 140 a to 140b can be equally circumferentially spaced around the glass filamentsupport (stem) 130 (FIG. 3B). A first end of each LED-filament 140 a to140 d distal to the connector base 110 is electrically and mechanicallyconnected to a first conducting wire 160 that passes down an axis of theLED filament support 130 to the connector base 110. A second end of eachLED-filament 140 a to 140 d proximal to the connector base 110 iselectrically and mechanically connected to a second conducting wire 170that passes through a base portion 180 of the LED filament support 130to the connector base 110.

An LED-filament 140 according to an embodiment of the invention is nowdescribed with reference to FIGS. 4A and 4B which shows across-sectional side view through A-A and a partial cut-away plan of anLED-filament. The LED filament 140 comprises a light-transmissivecircuit board (substrate) 200 having an array of blue emitting (dominantwavelength typically ˜450 to ˜460 nm) unpackaged LED chips (dies) 210mounted directly to one face. In the embodiment, illustrated the circuitboard 200 is planar and has an elongate form (strip) with the LED chips210 being configured as a linear array along the length of thesubstrate. An elongate array may be preferred when the LED-filament 200is used as a part of an energy efficient bulb since the appearance andemission characteristics of the device more closely resembles atraditional filament of an incandescent bulb. Depending on theapplication the circuit board can comprise other forms such as forexample being square or circular and the LED chips configured as otherarrays or configurations. It should be noted that the LED chips 210 aremounted directly to the circuit board 200 and are not packaged. Suchpackaging would otherwise block the emission of light in a backwarddirection towards and through the circuit board 200. Furthermore, itshould be noted that the light-transmissive substrate may have atransmittance in a range of 20% to 100% in the visible light spectrum.

Typically each LED-filament comprises fifteen LED 65 mW chips with atotal nominal power of about 1 W.

The circuit board 200 can comprise any light-transmissive material whichis at least translucent and preferably has a transmittance to visiblelight of 50% or greater. Accordingly, the circuit board can comprise aglass or a plastics material such as polypropylene, silicone or anacrylic. To aid in the dissipation of heat generated by the LED chips210, the circuit board 200 is not only light-transmissive but isadvantageously also thermally conductive. Examples of suitablelight-transmissive thermally conductive materials include: magnesiumoxide, sapphire, aluminum oxide, quartz glass, aluminum nitride anddiamond. The transmittance of the thermally conductive circuit board canbe increased by making the circuit board thin. To increase mechanicalstrength, the circuit board can comprise a laminated structure with thethermally conductive layer mounted on a light-transmissive support suchas a glass or plastics material. To further assist in the dissipation ofheat the volume within the glass envelope is preferably filled with athermally conductive gas such as helium, hydrogen or a mixture thereof.

The circuit board 200 further comprises electrically conductive tracks220 configured in a desired circuit configuration for electricallyconnecting the LED chips 210. As illustrated the LED chips 210 of theLED filament can be connected serially as a string and the LED filaments140 a to 140 b connected in parallel. It will be appreciated that othercircuit configurations can be used. The electrically conductive tracks220 can comprise copper, silver or other metal or a transparentelectrical conductor such as indium tin oxide (ITO). As illustrated theLED chips 210 are electrically connected to the conducting tracks 220using bond wires 230. In other embodiments, the LED chip can comprisesurface mountable or flip-chip devices. The LED chips 210 can be mountedto the circuit board by soldering, a thermally conductive adhesive or byother fixing methods which will be apparent to those skilled in the art.Where the light-transmissive circuit board 200 comprises a thermallyconductive material the LED chips 210 are advantageously mounted inthermal communication with the circuit board. A heat sink compound suchas beryllium oxide can be used to aid in thermal coupling of the LEDchips to the circuit board.

The LED-filament 140 further comprises a photoluminescence wavelengthconversion material 240 comprising a mixture of, for example a yellow togreen emitting (peak emission wavelength 520 nm to 570 nm) and anarrow-band red emitting (600 nm to 640 nm, FWHM 50 nm to 55 nm) CSSphosphor materials directly to the LEDs chips 210 in the form of anencapsulating layer.

In operation, blue excitation light generated by the LED chips 210excites the yellow to green-emitting and red-emitting phosphors togenerate yellow to green and red photoluminescence light. The emissionproduct of the LED-filament which appears white in color comprises thecombined photoluminescence light and unconverted blue LED light. Sincethe photoluminescence light generation process is isotropic, phosphorlight is generated equally in all directions and light emitted in adirection towards the circuit board can pass through the circuit boardand be emitted from the rear of the device. It will be appreciated thatthe use of a light-transmissive circuit board (substrate) enables thedevice to achieve a generally omnidirectional emission characteristic.Additionally, particles of a light reflective material can be combinedwith the phosphor material to reduce the quantity of phosphor requiredto generate a given emission product color. Furthermore, it isunderstand that the color of the light emitted by the bulb can bechanged by combining a different phosphor, or no other phosphor with thenarrow-band red phosphor.

LED-Filament Lamps: B-Series (B11) Bullet Lamp

FIGS. 5A and 5B respectively illustrate a partial cross-sectional sideview through C-C and a partial cutaway plan view of an LED-filamentB-Series bullet lamp (candle bulb) 300 in accordance with an embodimentof the invention. The LED-filament lamp 300 is intended to be an energyefficient replacement for an incandescent B11 bullet light bulb and isconfigured to generate 450 lm of light with a CCT (Correlated ColorTemperature) of 2700 K and a CRI Ra of 90 and CRI R9>50. As is known,the B11 bullet lamp is 1⅜ inches (11/8) wide at its widest point. TheLED-filament lamp 300 comprises four 1 W LED-filaments and is nominallyrated at 4 W. The LED-filament lamp 300 is essentially the same as theA19 LED-filament lamp 100 described in relation to FIGS. 3A, 3B, 4A and4B and like reference numerals are used to denote like parts.

As illustrated, the LED-filament lamp 300 can comprise an E12 (ϕ12 mm)connector base (Edison screw lamp base) 110. If practicable, theconnector base 110 can house driver circuitry (not shown) for operatingthe LED-filaments. Where it is impracticable to house the drivercircuitry in the connector base 110 the LED-filament lamp 300 canfurther comprise an extender 190 disposed between the envelope 120 andconnector base 110, as shown in FIG. 6. The extender 190 can comprise ahollow frusto-conical element comprising a plastics material.

Light emitting devices of the present invention have been describedherein as LED-filaments including a light-transmissive substrate whichis elongate in form, also as devices with an array of blue LED chipsmounted on the light-transmissive substrate, and also as devices withLED chips mounted on only one side of the substrate. However, in otherembodiments the light-transmissive substrate may be circular, square, orone of many other shapes, the device may have only a single LED chip, orjust two LED chips, mounted on a light-transmissive substrate, and LEDchips may be mounted on both sides of a light-transmissive substrate.

LED-Filament Lamp Test Data: A19 Lamp

FIGS. 7-11 show measured test data versus time after lamp turn-on for afour LED-filament A19 lamp in accordance with an embodiment of theinvention having an LED-filament comprising a green aluminate phosphor(GAL535)+a narrow-band red phosphor (CSS626). Note that the notationGAL535 used herein represents the phosphor type (GAL)—phosphors ofgeneral composition Lu₃Al₅O₁₂:Ce (i.e. LuAG—based)—followed by the peakemission wavelength in nanometers (535). Each figure also showscomparative data for a four LED-filament A19 lamp with an LED-filamentcomprising GAL535+a red phosphor (CASN630). As described above, CASN rednitride phosphor (Calcium Aluminum Silicon Nitride—general compositionCaAlSiN₃:Eu²⁺) is the most commonly used red-emitting phosphors in LEDapplications due to its high reliability and brightness.

Tables 1 and 2 tabulate measured test data for four LED-filament A19lamp with LED-filaments comprising i) GAL535+CSS626 and ii)GAL535+CASN630. Table 1 comprises test data that is measured 15 secondsafter lamp turn-on.

TABLE 1 Measured test data for a nominal 550 lm, 2700 K, 90 CRI Ra, FourLED-filament A19 Lamp Data measured 15 seconds after lamp Turn-On PowerFlux Efficacy CCT CRI LED-filament composition (W) (lm) (lm/W) CIE x CIEy (K) Ra R9 GAL535 + CSS626 3.98 576.4 144.8 0.4722 0.4212 2615 89.525.9 GAL535 + CASN630 4.04 592.3 146.5 0.4708 0.4282 2685 82.4 6.8

Table 2 comprises test data that is measured 15 minutes after lampturn-on (i.e. once the light emission of the lamp has stabilized).

TABLE 2 Measured test data for a nominal 550 lm, 2700 K, 90 CRI Ra, FourLED-filament A19 Lamp Data measured 15 minutes after lamp Turn-On PowerFlux Efficacy CCT CRI LED-filament composition (W) (lm) (lm/W) CIE x CIEy (K) Ra R9 GAL535 + CSS626 3.91 538.7 137.8 0.4644 0.4212 2919 87.919.4 GAL535 + CASN630 3.97 554.6 139.8 0.4674 0.4259 2713 81.8 4.8

Compared with an LED-filament comprising a CASN phosphor it can be seen(Table 2) that an LED-filament and/or LED-filament lamp in accordancewith the invention comprising a CSS phosphor can generate light with aCRI Ra of about 90 (˜88). Moreover, an LED-filament in accordance withthe invention can substantially increase CRI R9 by about fifteen toabout nineteen compared with an LED-filament comprising a CASN phosphorin which CRI R9 is about five (˜4.8). As indicated in Table 2, use of aCSS phosphor can result in a small decrease in luminous flux (˜3%: 554.6lm→538.7 lm) and a small decrease of luminous efficacy (˜1%:139.8→137.8). However, these decreases are far outweighed by thesignificant increase in CRI Ra and CRI R9 and such small decreases inbrightness/efficacy are acceptable in LED-filament lamps where lightquality matters more than overall light output.

FIG. 7 shows measured luminous flux (lm) versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) GAL535+CSS626 and ii) GAL535+CASN630. As can be seen in FIG. 7, theluminous flux (Brightness) for LED-filament lamps comprising CSSphosphor or CASN phosphor each reach a stable value after astabilization period of about 400 s from lamp turn-on and show about a6% decrease in luminous flux during the stabilization period. Afterstabilizing, the luminous flux for i) an LED-filament comprising CASNphosphor is approximately only 3% greater than ii) an LED-filamentcomprising CSS phosphor, which it will be appreciated is a minimaldifference.

FIG. 8 shows measured luminous efficacy (lm/W) versus time (s) afterlamp turn-on, for a four LED-filament A19 lamp with LED-filamentscomprising i) GAL535+CSS626 and ii) GAL535+CASN630. As can be seen inFIG. 8, the luminous efficacy for LED-filament lamps comprising CSSphosphor or CASN phosphor each reach a stable value after astabilization period of about 400 s and show about a 6% decrease inluminous efficacy over the stabilization period. After stabilizing, theluminous efficacy for i) an LED-filament comprising CASN phosphor isapproximately only 1.4% greater than ii) an LED-filament comprising CSSphosphor, which it will be appreciated is a minimal difference.

FIG. 9 shows measured general Color Rendering Index (CRI Ra) versus time(s) after lamp turn-on, for a four LED-filament A19 lamp withLED-filaments comprising i) GAL535+CSS626 and ii) GAL535+CASN630. As canbe seen in FIG. 9, the general CRI Ra for i) an LED-filament lampcomprising CSS phosphor reaches a stable value after about 300 s,compared with ii) an LED-filament lamp comprising CASN phosphor thatreaches a stable value after about 400 s. The general CRI Ra for i) anLED-filament lamp comprising CSS phosphor decreases about 1.5% (89.5→88)during the stabilization period, while ii) an LED-filament lampcomprising CASN phosphor decreases about 0.5% (82.5→82) during thestabilization period. It should be noted that after stabilizing i) anLED-filament comprising CSS phosphor CRI Ra is close to 90 (˜88) and issignificantly greater than ii) an LED-filament comprising CASN phosphorin which CRI Ra is close to 80 (˜82).

FIG. 10 shows measured chromaticity CIE x versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) GAL535+CSS626 and ii) GAL535+CASN630. As can be seen in FIG. 10, thechromaticity CIE x for LED-filament lamps comprising CSS phosphor orCASN phosphor each reach a stable value after a stabilization period ofabout 400 s. The chromaticity CIE x for an LED-filament lamp comprisingCSS phosphor decreases (Δ CIE x) about 0.0035 (0.4710→0.4675) during thestabilization period, compared with an LED-filament lamp comprising CASNphosphor in which CIE x decreases (ΔCIE x) about 0.0077 (0.4722→0.4645)during the stabilization period.

FIG. 11 shows measured chromaticity CIE y versus time (s) after lampturn-on, for a four LED-filament A19 lamp with LED-filaments comprisingi) GAL535+CSS626 and ii) green aluminate phosphor GAL535+CASN630. As canbe seen in FIG. 11, the chromaticity CIE y for an LED-filament lampcomprising CSS phosphor is stable from initial turn-on of the lamp andCIE y shows no measurable change over a period of 900 s from turn-on. Incontrast, the chromaticity CIE y for an LED-filament lamp comprisingCASN phosphor only reaches a stable value after a stabilization periodof about 400 s. The chromaticity CIE y for an LED-filament lampcomprising CASN phosphor decreases (Δ CIE y) about 0.0022(0.4282→0.4260) during the stabilization period.

Compared with an LED-filament lamp comprising a CASN phosphor, it can beseen (FIGS. 7 to 11 and Table 2) that LED-filaments and LED-filamentlamps in accordance with the invention comprising a CSS phosphor canincrease CRI Ra by about six and generate light emission with a CRI Raof about 90. Moreover, as can be seen from Table 2, LED-filaments andLED-filament lamps in accordance with the invention comprising a CSSphosphor (˜20) can increase CRI R9 by about fifteen compared with anLED-filament lamp comprising a CASN phosphor (˜4.8). It is indicated inFIGS. 7 and 8 and Table 2 that use of a CSS phosphor can result in asmall decrease in luminous flux (˜3%) and luminous efficacy (˜1%).However, these decreases are negligible compared with the significantincrease in CRI Ra and CRI R9 and such decreases are generallyacceptable in LED-filament lamps where quality of light matters morethan overall light emission brightness. Moreover, as can be seen fromFIGS. 10 and 11, LED-filaments and LED-filament lamps in accordance withthe invention comprising a CSS phosphor have a more stable chromaticity(quality of light color) during the stabilization period from lampturn-on compared with LED-filament lamps comprising a CASN phosphor. Insummary, measured test data shows that LED-filaments and LED-filamentlamps in accordance with the invention comprising a CSS phosphor cangenerate light with a CRI Ra of about 90, significantly increase CRI R9,have a more stable chromaticity during a stabilization period afterturn-on and have substantially the same performance and efficacy asLED-filament lamps comprising a CASN phosphor.

Table 3 tabulates measured test data for a nominal 800 lm, 2700 K, 90CRI Ra, Six LED-filament A19 lamp with LED-filaments comprisingGAL520+CSS626 at i) 20 seconds after lamp turn-on and ii) 15 minutesafter lamp turn-on (i.e. once stabilized). It can be seen from Table 3,that as with the test data for a four LED-filament A19 lamp discussedabove, a Six LED-filament lamp in accordance with the invention cangenerate light with a CRI Ra of about 90 (˜88) and a CRI R9 of about 20.

TABLE 3 Measured test data for a nominal 800 lm, 2700 K, 90 CRI Ra, SixLED-filament A19 Lamp with LED-filaments comprising GAL520 + CSS626 Timeafter lamp Flux Efficacy CCT CRI turn-on Power (W) (lm) (lm/W) CIE x CIEy (K) Ra R9 20 seconds 7.02 931.5 132.74 0.4662 0.4198 2683 89.7 27.3 15minutes 6.85 847.5 123.77 0.4575 0.4200 2806 88.3 20.3

Table 4 tabulates measured test data for a nominal 500 lm, 2700 K, 90CRI Ra, four LED-filament A19 lamp with LED-filaments comprisingGAL535+CSS628 at i) 20 seconds after lamp turn-on and ii) 15 minutesafter lamp turn-on (i.e. once stabilized). FIGS. 12-14 show reliabilitydata for the four LED-filament A19 lamp of Table 4 (i.e. LED-filamentscomprising GAL535+CSS628) operated at an ambient temperature of 25° C.FIG. 12 shows relative luminous flux versus time (hours). The relativeluminous flux is the luminous flux at time t compared with the luminousflux at t=15 minutes (i.e. once lamp has stabilized after initialturn-on). FIG. 13 shows change of chromaticity Δ CIE x versus time(hours) and FIG. 14 shows change of chromaticity Δ CIE y versus time(hours). The change of chromaticity Δ CIE x, Δ CIE y is the chromaticityand time t compared with the chromaticity at time t=15 minutes. As canbe seen from FIG. 12, the relative luminous flux changes less than ±2%over 3000 hours of operation. FIGS. 13 and 14 indicate that thechromaticity (quality of light color) of light generated by the lamp isvery stable over 3000 hours of operation with changes in CIE x and CIE yof less than ±0.001.

TABLE 4 Measured test data for a nominal 500 lm, 2700 K, 90 CRI, 25 CRIR9 Four LED-filament A19 Lamp with LED-filaments comprising GAL535 +CSS628 Time after lamp Flux Efficacy CCT CRI turn-on Power (W) (lm)(lm/W) CIE x CIE y (K) Ra R9 15 seconds 4.00 570.3 142.6 0.4754 0.42082572 90.0 28.9 15 minutes 3.92 529.7 135.1 0.4670 0.4211 2684 88.4 22.3

LED-Filament Lamp Test Data: B11 Lamp

Tables 5 to 8 tabulate measured test data for various four LED-filamentB11 lamps in accordance with the invention. Table 5 tabulates measuredtest data for B11 lamps (Samples 1 and 2) with LED-filaments inaccordance with the invention comprising GAL535+CSS634. It should benoted from Table 5 that by using a single CSS phosphor with a longerpeak emission wavelength (634 nm), it is possible to generate light witha CRI R9 of greater than 50 and a CRI Ra of greater than 90.

TABLE 5 Measured Test data for nominal 2700 K, 90 CRI Ra, FourLED-filament B11 Lamps with LED-filaments comprising: GAL535 + CSS634Pow- er Flux Efficacy CCT CRI Sample (W) (lm) (lm/W) CIE x CIE y (K) RaR9 1 4.04 439.8 108.8 0.4602 0.4234 2793 93.0 55.0 2 4.00 443.2 110.90.4622 0.4238 2769 93.3 54.5 Average 4.02 441.5 109.9 0.4612 0.4236 278193.2 54.8

Table 6 tabulates measured test data for B11 lamps (Samples 1-3) withLED-filaments in accordance with the invention comprising GAL535+mixtureof 90 wt. % CSS626 and 10 wt. % CSS634.

TABLE 6 Measured test data for nominal 450 lm, 2700 K, 90 CRI Ra, FourLED-filament B11 Lamps with LED-filaments comprising: GAL535 + mixtureof 90 wt. % CSS626 & 10 wt. % CSS634 Sam- Power Flux Efficacy CCT CRIple (W) (lm) (lm/W) CIE x CIE y (K) Ra R9 1 4.05 468.4 115.7 0.46130.4217 2765 90.0 33.7 2 4.01 463.1 115.5 0.4610 0.4225 2776 90.0 34.0 34.02 463.7 115.5 0.4619 0.4206 2748 90.1 35.1

Table 7 tabulates measured test data for B11 lamps (Samples 1-3) withLED-filaments in accordance with the invention comprising GAL535+mixtureof 70 wt. % CSS626 and 30 wt. % CSS634.

TABLE 7 Measured test data for nominal 2700 K, 90 CRI Ra, FourLED-filament B11 Lamps with LED-filaments comprising: GAL535 + mixtureof 70 wt. % CSS626 & 30 wt. % CSS634 Pow- er Flux Efficacy CCT CRISample (W) (lm) (lm/W) CIE x CIE y (K) Ra R9 1 3.31 382.4 115.7 0.46490.4215 2715 92.3 42.5 2 3.21 366.9 114.5 0.4645 0.4213 2718 92.4 43.1 33.23 369.5 114.5 0.4645 0.4212 2716 92.4 43.8 Average 3.25 372.9 114.90.4646 0.4214 2716 92.4 43.1

For ease of comparison and to illustrate the effects of using a mixtureof CSS phosphors with differing peak emission wavelengths, Table 8tabulates measured test data for B11 lamps with LED-filaments inaccordance with the invention comprising i) GAL535+CSS634, ii)GAL535+mixture of 90 wt. % CSS626 and 10 wt. % CSS634, and iii)GAL535+mixture of 70 wt. % CSS626 and 30 wt. % CSS634.

TABLE 8 Measured test data for nominal 450 lm, 2700 K, 90 CRI FourLED-filament B11 Lamps: Data measured 10 minutes after lamp Turn-On(Stabilized) Power Flux Efficacy CCT CRI LED-filament composition (W)(lm) (lm/W) CIE x CIE y (K) Ra R9 GAL535 + CSS634 4.02 441.5 109.80.4612 0.4236 2781 93.2 54.7 GAL535 + (90 wt. % CSS626 4.03 465.1 115.50.4614 0.4216 2763 90.0 34.3 & 10 wt. % CSS634) GAL535 + (70 wt. %CSS626 3.25 372.9 114.9 0.4646 0.4213 2716 92.4 43.2 & 30 wt. % CSS634)

FIGS. 15-18 show measured test data versus time after lamp turn-on for afour LED-filament B11 lamp with LED-filaments comprising a mixture(blend) of at least two narrow-band red CSS phosphors with differentpeak emission wavelengths. Each figure also includes comparative testdata for a four LED-filament B11 lamp with an LED-filament comprising asingle CSS phosphor.

FIG. 15 shows measured test data, luminous efficacy (lm/W) versus time(s) after lamp turn-on, for a four LED-filament B11 lamp withLED-filaments comprising i) GAL535+CSS626, ii) GAL535+narrow-band redphosphor (mixture of 90 wt. % CSS626 & 10 wt. % CSS634), and iii)GAL535+narrow-band red phosphor (mixture of 70 wt. % CSS626 & 30 wt. %CSS634). As can be seen in FIG. 15, the luminous efficacy forLED-filament lamps comprising i) a single CSS phosphor (CSS626) andlamps comprising ii) and iii) a mixture of CSS phosphors (CSS626 &CSS634), reach a stable value after a stabilization period of about300-500 s after lamp turn-on. The luminous efficacy for i) anLED-filament lamp comprising a single CSS phosphor decreases about 8%(119 lm/W→109 lm/W) during the stabilization period, while LED-filamentlamp comprising a mixture of CSS phosphors ii) and iii) respectivelydecrease about 7% (124 lm/W→115 lm/W) and about 3% (119 lm/W→115 lm/W)during the stabilization period. Compared with an LED-filamentcomprising a single CSS phosphor (CSS626), it can be seen (FIG. 15) thatafter stabilization an LED-filament and/or an LED-filament lamp inaccordance with the invention comprising a mixture of CSS (CSS626 andCSS634) phosphors that have different peak emission wavelengths (626 nm,634 nm) can increase the luminous efficacy of the lamp by about 5 lm/W(110→115 lm/W) that is about 5%.

FIG. 16 shows test data, Color Rendering Index (CRI) Ra versus time (s)after lamp turn-on, for a four LED-filament B11 lamp with LED-filamentscomprising i) GAL535+CSS626, ii) GAL535+narrow-band red phosphor(mixture 90 wt % CSS626 & 10 wt % CSS634), and iii) GAL535+narrow-bandred phosphor (mixture 70 wt % CSS626 & 30 wt % CSS634). As can be seenin FIG. 16, CRI Ra for each of the lamps reaches a stable value afterabout 300 and 400 s of lamp turn-on. For an LED-filament lamp comprisingi) a single CSS626 phosphor CRI Ra is about 93 after stabilization whileLED-filaments comprising a mixture of CSS626 & CSS634 phosphors, CRI Rais ii) about 90.0 and iii) 92.5 respectively. It can be seen thereforefrom FIG. 16 that an LED-filament in accordance with the inventioncomprising a mixture of CSS phosphors that have different peak emissionwavelengths can, compared with an LED-filament comprising a single CSSphosphor, increase the luminous efficacy of the lamp by about 5 lm/W(˜5%) while still maintaining a CRI Ra of at least 90 afterstabilization. Moreover, as can be seen from Table 8, this increase inluminous efficacy of the lamp is at the expense of a small decrease inCRI R9 (55→34/44).

FIG. 17 shows test data, chromaticity CIE x versus time (s) after lampturn-on, for a four LED-filament B11 lamp with LED-filaments comprisingi) GAL535+CSS626, ii) GAL535+narrow-band red phosphor (mixture of 90 wt.% CSS626 & 10 wt. % CSS634), and iii) GAL535+narrow-band red phosphor(mixture of 70 wt. % CSS626 & 30 wt. % CSS634). As can be seen in FIG.17, the chromaticity CIE x for LED-filament lamps comprising CSSphosphor or a mixture of CSS phosphors (CSS626 & CSS634) each reach astable value after a stabilization period of about 200-500 s. Thechromaticity CIE x for LED-filament lamps comprising a mixture of CSSphosphor decreases (ΔCIE x) during the stabilization period is ii) about0.0085, (0.4700→0.4615) and iii) about 0.0072 (0.4722→0.4650) comparedwith an LED-filament lamp comprising a single CSS626 phosphor in whichCIE x decreases (ΔCIE x) about 0.0122 (0.4722→0.4600) during thestabilization period.

FIG. 18 shows test data, chromaticity CIE y versus time (s) after lampturn-on, for a four LED-filament B11 lamp with LED-filaments comprisingi) GAL535+narrow-band red phosphor (CSS626), ii) GAL535+narrow-band redphosphor (mixture of 90 wt. % CSS626 & 10 wt. % CSS634), and iii)GAL535+narrow-band red phosphor (mixture of 70 wt. % CSS626 & 30 wt. %CSS634). As can be seen in FIG. 18, the chromaticity CIE y forLED-filament lamps comprising CSS phosphor or a mixture of CSS phosphors(CSS626 & CSS634) stabilize after a stabilization period of about200-500 s. The chromaticity CIE y for a LED-filament lamps comprising amixture of CSS phosphor increase (ΔCIE y) during the stabilizationperiod ii) about 0.0009 (0.4208→0.4217) and iii) 0.0003 (0.4212→0.4215),compared with an LED-filament lamp comprising a single CSS626 phosphorin which CIE y increases (ΔCIE y) about 0.0014 (0.4220→0.4234) duringthe stabilization period. As can be seen from FIGS. 17 and 18,LED-filaments and LED-filament lamps in accordance with the inventioncomprising a mixture of at least two CSS phosphors, have a more stablechromaticity CIE x and CIE y (quality of light color) during thestabilization period after lamp turn-on compared with anLED-filament/lamp comprising a single CSS phosphor.

In summary, LED-filaments and/or LED-filament lamps in accordance withthe invention that comprise a mixture of at least two CSS phosphorshaving different peak emission wavelengths can, compared with anLED-filament comprising a single CSS phosphor, have a more stablechromaticity (quality of light color) during the stabilization periodafter lamp turn-on, increase the luminous efficacy of the lamp whilestill maintaining a CRI Ra of at least 90 and with only a small decreasein CRI R9.

Comparative Data Using Cavity Phosphor Test

Tables 9 to 12 tabulate measured phosphor cavity test data to show theeffect of red phosphor composition. The cavity test method involvesmixing the phosphor powder with an uncurable optical encapsulant andplacing the mixture in a cavity containing a blue LED (dominantwavelength 452 nm) and measuring total light emission in an integratingsphere. The data in these tables further illustrates the benefits ofusing a mixture of CSS phosphor(s) as compared with using a CASNphosphor in LED-filament applications having a CRI Ra of at least 90.

Table 9 tabulates measured test data for a 5630 (5.6×3.0 mm package)cavity comprising i) GAL535+CASN628, ii) GAL535+CASN630, and iii)GAL535+CASN640 and illustrates the effects of red phosphor compositionon relative luminous flux (%), CRI Ra and CRI R9. As can be seen fromTable 9, use of CASN phosphor with an increasingly longer peak emissionwavelength (628 nm, 630 nm, 640 nm) can simultaneously increase CRI Rafrom about 83 to about 92 and CRI R9 from about 8 to about 59. However,in the process of increasing CRI Ra to 90, the relative luminous flux(Brightness) drops by a massive 22%.

TABLE 9 5630 cavity comparing CRI Ra 80 and CRI Ra 90 devices FluxRelative CCT CRI Composition (lm) Flux (%) (K) Ra R9 GAL535 + CASN628103.4 100.0 2628 83.3 7.6 GAL535 + CASN630 100.5 97.2 2700 84.6 14.9GAL535 + CASN646 84.9 78.3 2700 92.1 59.3

Table 10 tabulates measured test data for a 2835 (2.8×3.5 mm package)cavity comprising i) GAL535+CASN628, and ii) GAL535+CASN645 andillustrates the effects of a red phosphor composition on relativeluminous flux (%), CRI Ra and CRI R9. Table 10 indicates that use ofCASN phosphor with a longer peak emission wavelength (628 nm→645 nm) cansimultaneously increase CRI Ra from about 83 to about 88 and canincrease CRI R9 from about 6 to about 48. However, and consistent withthe data for a 5630 cavity (Table 9), in the process of increasing CRIRa to 90, the luminous flux drops by a massive 18%.

TABLE 10 2835 cavity illustrating effect of red phosphor composition onBrightness, CRI Ra and CRI R9 Power Flux Efficacy Relative CCT CRIComposition (mW) (lm) (lm/W) Flux (%) CIE x CIE y (K) Ra R9 GAL535 +CSS628 181.2 16.8 113.3 100.0 0.4343 0.4125 3114 82.7 5.9 GAL535 +CSS645 180.6 20.5 93.0 81.8 0.4366 0.4160 3102 88.1 48.4

Table 11 tabulates measured test data for a 5630 cavity comprising i)GAL535+CSS626, ii) GAL535+mixture of 90 wt. % CSS626 & 10 wt. % CSS634,and iii) GAL535+mixture of 80 wt. % CSS626 & 20 wt. % CSS634 andillustrates the effects of a red phosphor composition on relativeluminous flux (%), CRI Ra and CRI R9.

TABLE 11 5630 cavity illustrating effect of red phosphor composition onBrightness, CRI Ra and CRI R9 Flux Relative CCT Composition (lm) Flux(%) CIE x CIE y (K) CRI R9 GAL535 + CSS626 13.02 100.0 0.4596 0.40982698 91.0 34.4 GAL535 + (90 wt. % CSS626 & 12.86 98.8 0.4603 0.4108 269692.3 41.6 10 wt. % CSS634) GAL535 + (80 wt. % CSS626 & 12.74 97.8 0.46030.4115 2701 92.9 44.7 20 wt. % CSS634)

Table 12 tabulates measured test data for a 5630 cavity comprising i)GAL535+CSS626 and ii) GAL535+mixture of 70 wt. % CSS626 & 30 wt. %CSS634 and illustrates the effects of red phosphor composition onrelative luminous flux (%), CRI Ra and CRI R9.

TABLE 12 5630 cavity illustrating effect of red phosphor composition onBrightness, CRI Ra and CRI R9 Flux Relative CCT CRI Composition (lm)Flux (%) CIE x CIE y (K) Ra R9 GAL535 + CSS626 12.45 100.0 0.4607 0.41542725 90.0 31.0 GAL535 + (70 wt. % CSS626 & 12.10 97.2 0.4603 0.4131 271294.1 52.7 30 wt. % CSS634)

As can be seen from Tables 11 and 12, use of a mixture of CSS626 andCSS634 phosphors with an increasingly weight proportion of CSS634 (10%,20%, 30%) can simultaneously increase CRI Ra from about 90 to about 94and CRI R9 from about 31 to about 53. However, and in contrast to thedata for CASN phosphors (Tables 9 and 10) the use of a mixture of CSSphosphors enables CRI Ra and CRI R9 to be increased with only a smalldrop in relative luminous flux (Brightness) of less than about 3%.

In summary, the foregoing description shows that LED-filaments andLED-filament lamps comprising a narrow-band red phosphor, such as a CSSphosphor, are capable of generating light having i) a CRI Ra of 90 andgreater, ii) a CRI R9 up to about 55, and iii) a more stablechromaticity (quality of light color) during a stabilization periodafter turn-on while having substantially the same efficacy asLED-filament lamps comprising a CASN phosphor. This result is surprisingsince CSS phosphors are known to have poor reliability and problemsrelated to thermal quenching and blue quenching. For these reasons, suchphosphors are not used in LED applications. It is postulated that in anLED-filament, that comprises multiple low power LED chips (e.g. 15×16 mWLED-chips per filament), the blue power density is lower compared withan LED device comprising a single LED chip (e.g. 1 W) resulting in areduction of blue quenching. Moreover, it is postulated that sinceLED-filament lamps often comprise an inert gas such as helium, this mayresult in lower operating temperature than expected and that this resultin a reduction of thermal quenching. It is believed that it may be acombination of these factors that account for the unexpectedly goodperformance of CSS phosphors within LED-filaments and LED-filamentlamps.

Although the present invention has been particularly described withreference to certain embodiments thereof, it should be readily apparentto those of ordinary skill in the art that changes and modifications inthe form and details may be made without departing from the spirit andscope of the invention. For example, LED-filaments in accordance withthe invention find application other bulb types such as generalmushroom, elliptical, (E) and sign (S) bulb designs and decorativetwisted candle, bent-tip candle (CA and BA), flame (F), globe (G),lantern chimney (H) and fancy round (P) bulb designs.

What is claimed is:
 1. A light emitting device comprising: alight-transmissive substrate; at least one blue LED chip mounted on aface of said light-transmissive substrate; and a photoluminescencematerial at least partially covering said at least one blue LED chip,said photoluminescence material comprising phosphor particles of atleast one Group IIA/IIB selenide sulfide-based phosphor material;wherein said phosphor particles generate red light with a peak emissionwavelength in a range of 600 nm to 640 nm and a full width at halfmaximum emission intensity of 50 nm to 55 nm.
 2. The light emittingdevice of claim 1, wherein said Group IIA/IIB selenide sulfide-basedphosphor material has a composition MSe_(1-x)S_(x): Eu, wherein M is atleast one of Mg, Ca, Sr, Ba and Zn and 0<x<1.0.
 3. The light emittingdevice of claim 1, wherein said phosphor particles generate red lightwith a peak emission wavelength in a range of 624 nm to 628 nm.
 4. Thelight emitting device of claim 1, wherein said phosphor particlesgenerate red light with a peak emission wavelength of about 626 nm. 5.The light emitting device of claim 1, wherein individual ones of saidphosphor particles comprise an impermeable coating.
 6. The lightemitting device of claim 5, wherein said impermeable coating comprisesone or more materials chosen from the group consisting of: amorphousalumina, aluminum oxide, silicon oxide, titanium oxide, zinc oxide,magnesium oxide, zirconium oxide, boron oxide, chromium oxide, calciumfluoride, magnesium fluoride, zinc fluoride, aluminum fluoride andtitanium fluoride.
 7. The light emitting device of claim 1, wherein saidlight emitting device is characterized by CRI Ra of greater than orequal to
 90. 8. The light emitting device of claim 7, wherein said lightemitting device is further characterized by a CRI R9 of greater than orequal to
 50. 9. The light emitting device of claim 1, wherein saidphosphor particles comprise first particles with a first peak emissionwavelength in a range of 624 nm to 628 nm and second particles with asecond peak emission wavelength in a range of 630 nm to 638 nm.
 10. Thelight emitting device of claim 9, wherein said light emitting device ischaracterized by a CRI Ra of greater than or equal to 90 and a CRI R9 ofgreater than or equal to
 50. 11. The light emitting device of claim 10,wherein said first peak emission wavelength is about 626 nm and saidsecond peak emission wavelength is about 634 nm.
 12. The light emittingdevice of claim 11, wherein said photoluminescence material furthercomprises particles of a yellow to green-emitting phosphor thatgenerates yellow to green light with a peak emission wavelength in arange of 520 nm to 570 nm.
 13. The light emitting device of claim 12,wherein said yellow to green-emitting phosphor generates green lightwith a peak emission wavelength in a range of 520 nm to 540 nm.
 14. Thelight emitting device of claim 1, wherein at least a part of saidlight-transmissive substrate comprises a material selected from thegroup consisting of magnesium oxide, sapphire, aluminum oxide, quartzglass, aluminum nitride and diamond.
 15. The light emitting device ofclaim 1, wherein said light-transmissive substrate is elongate in form.16. A lamp comprising: a light-transmissive envelope; and at least onelight emitting device located within said light-transmissive envelope,said light emitting device comprising: a light-transmissive substrate;at least one blue LED chip mounted on a face of said light-transmissivesubstrate; and a photoluminescence material at least partially coveringsaid at least one blue LED chip, said photoluminescence materialcomprising: phosphor particles of at least one Group IIA/IIB selenidesulfide-based phosphor material that generates red light with a peakemission wavelength in a range of 600 nm to 640 nm and a full width athalf maximum emission intensity of 50 nm to 55 nm; and phosphorparticles of a yellow to green-emitting phosphor that generates yellowto green light with a peak emission wavelength in a range of 520 nm to570 nm; wherein said lamp is operable to generate light with a colortemperature in a range of 1500 K to 4000 K and a CRI Ra of greater thanor equal to
 90. 17. The lamp of claim 16, further characterized bygenerating light with a CRI R9 of greater than or equal to
 50. 18. Thelamp of claim 16, wherein said light-transmissive envelope is filledwith an inert gas.
 19. The lamp of claim 18, wherein said inert gascomprises helium.
 20. The lamp of claim 16, wherein said Group IIA/IIBselenide sulfide-based phosphor material has a compositionMSe_(1-x)S_(x):Eu, wherein M is at least one of Mg, Ca, Sr, Ba and Znand 0<x<1.0.
 21. The lamp of claim 16, wherein said phosphor particlesgenerate red light with a peak emission wavelength in a range of 624 nmto 628 nm.
 22. The lamp of claim 16, wherein said phosphor particlesgenerate red light with a peak emission wavelength of about 626 nm. 23.The lamp of claim 16, wherein individual ones of said phosphor particlescomprise an impermeable coating.
 24. The lamp of claim 23, wherein saidimpermeable coating comprises one or more materials chosen from thegroup consisting of amorphous alumina, aluminum oxide, silicon oxide,titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, boronoxide, chromium oxide, calcium fluoride, magnesium fluoride, zincfluoride, aluminum fluoride, and titanium fluoride.
 26. The lamp ofclaim 16, wherein said phosphor particles comprise first particles witha first peak emission wavelength in a range of 624 nm to 628 nm andsecond particles with a second peak emission wavelength in a range of630 nm to 638 nm.
 27. The lamp of claim 26, wherein said first peakemission wavelength is about 626 nm and said second peak emissionwavelength is about 634 nm.
 28. The lamp of claim 16, wherein saidyellow to green-emitting phosphor generates green light with a peakemission wavelength in a range of 520 nm to 540 nm.
 29. The lamp ofclaim 16, wherein at least a part of said light-transmissive substratecomprises a material selected from the group consisting of magnesiumoxide, sapphire, aluminum oxide, quartz glass, aluminum nitride, anddiamond.
 30. The lamp of claim 16, wherein said light-transmissivesubstrate is elongate in form.